Efficiency meter



Patented Aug.` 12, 1941 EFFICIENCY :METER Wilhelm E. Germer,Berlin-Charlottenburg, Germany Application August 27, 1938, Serial No.227,136 In Germany August 21, 1937 9 Claims.

This 'inventionl relates to an efdclency meter i and more particularlyto an apparatus for the determination of the most favorable operation ofboilers and for the determination and continualyindication of the rateof veiliciency and the ilue gas loss of a boiler in percent.

The economic operation and the correct conj trol of a 'boiler is basedat present mainly upon the continual testof the ilue gases, taken at apoint in the passes of the boiler, where the combustion has just .beencompleted. The percentage of CO2 and of (CO+H2) or lof Oz and(C'O-l-Hz), indicated continually by al gas analyzer, permits thedetermination of the amount of excess air, used for the combustion andserves in addition to indicate Whether the combustion in the boiler hasbeen completeI or incomplete.

4The stratification of the ilue gases in connec.

tion With the lag of the gas analyzer makesythis determinationdoubtfuland gives the boiler operator no reliable guide to find and maintain themost favorable operation of the boiler.

Attempts have been made to overcome this difficulty by taking thedifferential draft at two. points of the boiler', for instance the draftloss between the second and third pass, as a measure of the amount offluergas ow and compar-I ing thisv amount continuously. with thegenerated amount of steam. By various and elaborate boiler tests, onetries to iind that relation between ilue gas amiV steam ilow,that willprovide the best operation of the boiler'. Control may be eiected byvutilizing steam ow vand gas flow meters adjusted so that their pointerswill coincide at the best operation oi the boiler, as

shown by the tests, and by adjusting/the air flow from time to time tokeep the pointers together.

It is hardly possible, however, to determine the most favorablecombustion and the best air ow with this method, as such boiler testshave to bel carried-through over long periods of time at constant load,and constant excess air. in order to give somewhat reliable results. Itis therefore nearly impossiblef to determine accurately in such a waythe best air owat various amounts oi excess air for diil'erent loads.This method y of boiler control has the particular disadvantage that ailxed relation is established between steam and air iiow. This is notcorrect-as this relation changes rapidly as soon as the condition of theboiler changes. Deposits of the feed water in the tubes or slagging ofthe tubes change at once the amount ofsteam at the same state of lcombustion, 4or the same air ilow. This leads to (Cl. 'za-196) l anincorrect operation of the boiler, not visible .5 ation of a boiler.

Another object of the invention is to provide an efiiciency meter whichprovides an accurate indication of the efficiency atl all times.According to one feature of the invention the efficiency is indicatedinstantaneously on a single instrument so that an operator can ascertainthe operating conditions at a glance.

Still another object of the invention is to provide an 'efficiency meterin which the eiliciency is determined by comparing the amount of usefulheat lin the steam with heat losses in the flue gas and by radiationand-the like. Preferably the determination is modified to compensate forunburnd gas leaving the boiler.

Other objects, advantages and novel features of the invention willappear as the description proceeds.

According to the method of the present invention a complete combustionin the boiler is assumed at first, the real rate ot iilciency oftheboiler is determined'for this condition and indicated continuously inpercent on a dial or recording instrument. In addition' the-totalpercentage of unburnt gases, such as CO or H2, will le determined fromilue gas samples taken in t e passes or in the nue gas channel andindicated `on an instrument having, a scale which permits the directreading oi' the correction required for the plus indication of the rateof etliciencyas soon as incomplete combustion takes place. The true rateof eiiiciency will thus alv ways be obtained. The (CD4-Hz) indicatorwill read zero, if a complete combustion exists.

The practical solution of the present method demands the continualdetermination of the heat energy ilowing-oil with the ilue gases and theheat energy used for the generation of the steam. l

The rlrst energy is found by:

` E1=RM.(Rt-t .cpm

and '760 mm. mercury between Rt and zero. This energy E1 is independentof the amount of secondary air contained in the flue gas atvthe point offlow measurement, as an'addition of secondary air increases the quantityofgas and decreases the temperature of the gas mixture, while theproduct for the heat energy E1 remains constant; s

According to the invention the nue gas measurement is accurately takenas a nozzle or orifice measurement in the flue or stack so as to include`all secondary air and all air filtering into the boiler and so as toobtain an accurate measure of flow unaffected by changes in the internalcondition of the boiler. The temperature measurement is preferably takenat the same point as the flow measurement and the flow measurement y ismultiplied by the difference in temperature between the flue gas and theair in the boiler --room to obtain an accurate measure of the heatenergy flowing out in the nue gas.

The'energy En used for the continuous generl ation of the steam isobtained by f Ez=D.(i-ts)A in which E1 signifies .the mm1 heatenergyiu'sea for the generation of the steam in kcaL/sec., D

n the steam now in lig/sec., i the neat' capacity of 1 kg. of steam inkcal. and ts the temperature of the feed water in degrees centigrade.'Since the heat capacity of saturated steam changes very little withchanges in pressure and since the changes inhe'at capacity of superlheated steam are substantially compensated by errors in an ordinary'orifice type of steam flow meter which is uncorrected for tempera-`ture, I have found that accurate results can be obtained by usingaconstant mean value of in. Changes in feed water temperature ts arerelatively small and infrequent and may easily be taken care of by acorrecting adjustment, preferably manual. Therefore, the energy E2 0fthe steam maybe indicated directly Vfor practical purposes by anuncorrected steam flow meter adjusted to compensate for the feedwaterteml pel'atllle.

If E signies the-total energy of th fuel in kcaL/sec. taking part in thecombustion, there still remains a third small part of energy Ea, aboutone half of which is due to losses in conductivity and radiation and theother half to losses o f unburnt fuel in the ashes, called the refuselosses. -These losses Acan be considered as nearly constant, as theydepend very little on the operation of the boiler and vary only between4V to6 percent. These losses can be determined partly by an ash analysisand partly be estimated empirically, according to the typei of theboiler.

For complete combustion the followingequation for the distribution ofthe fuel energy in' If 1; signiiies the rate of efficiency of the boilerin percent, Va the heat loss contained in the ue gases in percent, and athe sum of the constant losses in percent, one can write:

From these twoequations .the following relation may be derived:

As cpm and C'i-ts) may be considered as constant, one can substitute anew constant Q. "fc-1s) and can consider the rate of eiificiency of theboiler as a function of the quotient Denoting this variable quotientwith one obtains s: RMrm-z).

to give a direct efficiency reading.

Thequotient y l l nRM. (Rtt) III- T*M can also be considered as' thequotient between E1 and E2, that is the relation of the heat energyflowing oir with the flue gas and the heat energy used for thegeneration of the steam. As it is-possible to set:

and l A VE=B.Hu.

wherein B denotes the total burning fuel in kg.

per second and Hu the lower lheating value of the combustible in kcal.per kg., one, gets the 11 From thisv equation it is apparent that therelation of the two energies EizEa and in consequence thereof, themeasurement of the quotienta: as well as the measurement of the rate ofefficiency of the'boiler 11, is perfectly independent of any changes inor of the absolute size ofthe lower heating' value of the burningcombustible, as the total heat E=('B. Hu) disappears in the quotient.

The conditions described above change slightly if an incompletecombustion takes place, AIn

. this case a fourth part of energy E4 is supplied by the totl. energyE. This part contains the energy that corresponds to the heatingcapacity of the unburnt gases, mainly CO and Ha.

.which the scale of the quotient meter is based.,

Des-

heating value changes. The boiler operator has now an absolutelyreliable instrument indicating The efliciency meter indicates therefore.alittle too much, as the function y, "IH-x hasta be multiplied now withthe 'smaller factor: [100-(Vco+a)] instead of (10U-a). If 1, denotes theindicated value of theboiler efficiency by the quotient meter and mi thetrue rate of elllciency at incomplete combustion, 'the followingrelation exists:

Wherein b signifies a constant, p the percentage of unburnt gases(CO-l-Hz) of the flue gas at the end ,of the boiler and n the factor forthe I v excess air, givingthe relation of the actual air used for thecombustion'to the air required for theoretical combustion. The constantIJl depends somewhat on the lowerv heating value of the fuel, it'amountsto about 3.30 for solid combustibles with a lower heating value between3500 how to run the boiler and he sees at oncethe effect of any mistakeor change he has made in the operation. He has only to adjust the supplyof fuel to the demand of steam and to change the air until best elciencyis obtained. A bad condition of the 'boiler will be shown at once in alow rate of efficiency.

Asl the (CO-l-I-Iz) -meter serves only to indicate the plus error of therate of eiiiciency meter, a lag in indication is not so important hereand is permissible.

In a similar way the iiue gas loss can be indicated continuously inpercent by a quotient meter. From the ,two equations for the energy atcomplete combustiom one gets:

Inserting herein the kcal., one gets:

values for E1 and En in D oi-4S) HRMTf'-i) cpm for the' indication of Vais now:

10U-am Var-mf This quotient meter indicates thus the ilue gas loss Vainpercent directly. At'an incomplete combustion the quotient meter readstoo high 'Ihe quotient but can be corrected as before by a (CD4-H2)- and80,00 kcal. per kg. and is about 3.70 to 3.90

for soft brown coal with much moisture with a heating value between 1500and 3500 kcal. per kg. In view of the small absolute size ofthecorrections that have to be `taken care of by the (CO+H2)-metr, thevariable factors n forthe excess air andforthe boiler efiiciency n canbe replaced here by constant means values nm and nm, as the amount ofexcess air and the boiler eiilciency are known approximately for a giventype of boiler. 'Inserting these values, one gets the amount of' the4plus reading or the required correctionfor the eiciency meter:

7l.m.b.'i7, A fp ioo-a p With this constantfactor f andthe percentage ofunburnt gases p, one can give the scale of the (CO+I I2)`-meter directlya division for the reading of `these corrections, as the percent-scalehas only to be enlarged by f.

By this combination of a quotient meter rindicating the rate ofefficiency of the bonelfor perfectcombustion and a gas analyser forunburnt gases, indicating directly the necessary y corrections for theplus reading of the first meter, it is now possible to determineaccurately the most favorable state of combustion, which lies generallyLin Athe zone of incomplete combustion. The indication is correctregardless of the condition of the boiler itself, no matter what kind"of combustible is used, or how the lower meter, by using the average uegas loss Vam in the scale and by enlarging the percent-scale for(CO-i-Hz) by the factor Before giving any details of the quotient meterfor the -rate of efficiency, itis necessary to describe more exactly theintroduction of the temperature factors, represented by the values(Rt-t) and (z'ts) As generally the dilerential pressure method is takenfor the flue gas measurement in connection with a parabolic nozzle andaring balance or a flow meter of bell type with parabolic displacer orcurved disc, the

indicated flow will change with the flue gas4 temperature proportionalto the expression:

Rt@ -I- 273 V Rai Ali-273 which vcan be expanded into perature Rio willcause the following change in the product RM.(Rt-t):

As (Rte-t) is constant, the factor d is the total temperature factorwith which the flue gas ow RM has to be multiplied for the measurenientof the product. As

and as the second members of each of the two factors are small comparedto the value 1, one

can set for the temperature factor d very closely:

fluence of temperature changes, of the product RM-(Rt-t). With (Rta-t)as a constant, it is therefore: RM.(Rt-t)=RM.(1;i;m.At).(Rt0-t) Thetemperature factor (i-ts) of the steam flow contains the heat capacityz'. As mentioned above, a constant mean value io can be used. Thechanges of' i are too small for any changes in pressure, and thenecessary changes of i for any changes in temperature of superheatedsteam can easily be compensated by `the plus or minus reading of a steammeter of differential pressure type, having purposely no temperaturecorrecting element for the now indication. The constant value z'ocorresponds then -to that condition of steam temperature for which thesteam meter reads correctly. Consequently only the changes of-the feedwater temperature ts have to be considered in the measurement.

The changes in feed water temperatures are generally small compared tothe large value of io, so that it may frequently'be possible to neglectthese changes.

Introducing here, however, in a similar manper as before, a constantaverage feed water Itemperature tso and the'constant average heatcapacity in for `1 kg. of the steam and designat- 4'ing with 1- thedeviation ofthe' real feed water temperature ts from the mean value tso,the con- Yetant value (in-tst) will change by 1- for a givenV change of1F. It is then:

(itis) il (oist) :F f

1 l {WMM-80) (1 :FS--(io-tso) s'f-V) sions for the quotient :c and y forthe indications 6 of the rate of eiliciency and iiue gas loss can bewritten: v

RM.(Rt0-t) .(1 i mnt) cpm D q (FFSJ'V) (io-4%) M (1im.M) (Rt,-t).cpm D(Nien) (11,- iso) and correspondingly D (Is) (1:0- iso) y"RM (iimnt)(Ra-0.6m" In both expressions the last factor is constant.

Designating this last constant factor of the expression :c for a givenboiler with e, one-gets:

and the expressions for the quctients are at last simplied tothevfollowing values, upon which the actual measurement will be based:

, of boiler indication as so' far described is illustrated in theaccompanying drawing, in which:

Figure 1 is a diagrammatic view of a boiler with an indicating systemembodying the invention applied thereto;

Figure 2 illustrates aj modified arrangement for indicating theeiiiciency;

Figure 3 illustrates'a gas analyzer scalefor use with the presentinvention; and

Figure 4 illustrates a composite indicating instrument.

Figure 1 illustrates a boiler I0 supplied with fuel by a stoker I2, althugh itis to be understood that any suitable su ply means for supplyinggas','oil or the like@ the furnace might be employed. A- plurality ofwater tubes I4 are mounted in the boiler and are connected to a suitableheader or drum I6 from which a steam pipe I8 leads to any "desired steamconsuming apparatus. Baflles 2U divide the boiler into several passesterminating in a flue 22 connected to a suitable stack 'or the like.While one particular formlof boiler has been nlustrtea it win beunderstood that thisjis not material to the invention but that theinvention might be 'utilized with any desired type of boiler.

In *order to measure the steam ow from the boiler,zan orifice 24isplaced in the pipe I8 and has its opposite sides connected to a steamflow meter 26 which may be of any desired type. The meter "26 isconnected to a rod 28 and serves to move it vertically proportionally tovariations in steam flow. As pointed out above the meter 28 isuncorrected for temperature so that it automatically compensates forsuperheat. Y'll'hus the ro'd 2'8 -is moved proportionally to variationsin the quantity of heat flowing from the boiler in the steam.

` to a rod 40 Which is moved its inlet'side and its throat to a flowmeter 32.

A rod 34 has one enduconnected to the meter 32 to be moved therebyproportionally to variations in the ilow through ue 22.

The gas temperature isv measured by a thermometer 36 extending into theventuri 30so that gas ow and temperature are measured at the same point.A temperature responsive instrument 38 is connected to the thermometer36 and thereby proportionally to temperature changes. .v

Thesteam ow, gas ilow and gas temperature are'preferably separatelyindicated and since the indicating mechanisms may be identical only oneof them will be described in detail. As shown, the rod 28 is connectedto a pivoted wiper arm 42 which -is connected to one side of a batteryor the like 44, th`e other side of which is connected to one end of eachof two crossed coils 46. The other ends of the crossed coils 46 areconnected respectively to the opposite ends of a resistance 48 overwhich the wiper 42 moves. An arm 50 is operated Vby the coils 46jandmoves a pointer v52 over a scale 54 which is s -.tably calibrated interms of steam flow or of .the quantity of heat ilowing out in thesteam. Q'

As the arm 42 is moved by the meter 26 the,

effective resistance in circuit with each of the coils 46 is varied tocause a corresponding variation. in the relative effective strength ofthe coils Y so that the arm 50 vwill be moved. Thus the indication canreadily be carriedl to any desired point remote from the meter 26.

The rods 34 and 40 operate similar wiper arms 56 and 58 over similarresistances 60 and 62 to indicate gas ow and gas temperaturerespectively n scales 64 and 66.

The indicating mechanism also preferably includes means forautomatically solving the equations set out above to give a directindication of the instantaneous boiler eiiciency. As shown, each of therods 28, 34 and 40 operates a second wiper arm 68, 1 0 and 12 movingrespectively over resistances 14, 16 and 18. The resistance 'I4 has itsopposite ends connected to one of a pair of crossed coils 60 and' to theopposite ends of a resistance 82 whose centeris connected through 'arheostat 84 and an ammeter 85 to one side of a battery or the like 86.The rheostat 84 provides anA adjustment to set for the xed lossesthrough= radiation and the like corresponding to the energy E3 in theabove equations. Thel wiper arm 68 is connected through a rheostat 88 tothe opposite side ofthe battery 86, the rheostat 88 serving to set thefeed Water temperature and specific heat of the steam correspondingtothe quantity (i-ts) in the above rquations. Thus the one coil 80 willb energized proportionally to the quantity D (i-ts) or to the quantityof heat utilized in the generation of steam.

The resistance 'I6 has its opposite ends connected to the ends of theother crossed coil 80 and to the ends of a resistance 90 whose center isconnected through the rheostat 84 to one side of the battery 86. Thewiper arm 10 is connected to the resistance 18 and the wiper arm 12' isconnectedvto the other side of the battery.y Thus the other coil 80,wil1be energized proportionally to the product of gas'flow and gastemperature [RM (Rt-t) l. The whole circuit forms a bridge and togetherwith the crossed coils divides the heat energy of the gas by the heatenergy oi vthe steam to solve the quotient in the equations noted aboveso that by properly Calibrating the device the instantaneous eiiiciencycanbe indicated directly.l An arm 92 is mounted so as to move inresponse to the joint effects of the coils 80 to move a pointer 94 overafscale 96 which is suitably'calibrated in terms of eiciency.

If desired suitable adjustmentsof the rheostat 84 may be made to correctfor unburned gas (CO-l-Hz) as indicated by a gas analyzer. However, theerror in reading of the eiiiciency meter may itself be corrected ifdesired to obtain a correct value ofthe eiilciency. For this purpose agas analyzer 91 for measuring unburned gas may be provided with a scaleas indicated in Figure 3` in which the upper part of the scale, 98 readsdirectly in percent of unburned gas passing outv oi the furnace and thelower part of the 4scale. |00 reads directly in eillciency correction. Apointer |02 operated by the gas analyser A91 moves over both parts ofthe scale and to correctr the efficiency meter reading on scale 96 it isnecessary only to deduct the indicated,correc tion on the scale |00. y

Figure 2 indicates a mechanicalmethod for indicating the eiiciency inwhich a steam flow meter |04 connected to opposite sides of an oricesuch as 24operates a cam |06 which in turn moves a lever |08 and a scaleH0. A gas ilow meter ||2 connected to a venturi or thejlikel such as 30is l corrected for gas temperature and moves a cam I |4- proportionatelyto the product of gas ow and gas temperature. A lever 6 is operated bythe cam ||4 and moves a pointer I8 over the scale 0.

The cams |06 and ||4 give logarithmic motions to the scale ||0 and thepointer l|8 and .the scale is displaced to the right a distance equal tolog e as determined from the equations set out above. 'I'herefore theinstantaneous elciency is indicated directlyon scale ||0 by the pointer||8.

Figure 4l 4showsone form of rate of efficiency meter, developed as asimple double indicating instrument with two electric measuring systemsfor long distance transmission. One system in'- cludes a steam flow de e|20 responsive to steam ilow and connectedg to the pointer A to show thesteam ow onfthe upper D-scale, while the other includes a diierentialindicator |22 connected to a gas ow meter |24 and a gas temperatureresponsivel unit |26 and'operating a pointer B carrying a triangularscale C with a convergent scale F for the rate of efllciency. Thepointer B indicates the quantity of heat in the flue gas or the value ofthe product RM. (Rt-t) on the second instrument scale above. The RM.(Rt-t) scale'has been calculated in this example for a boiler with anaverage rate of emciertcy of '10% and the vertical line on theconvergent F-scale is marked 'I'he m'aximum value of the RM.(Rt-t) scaleof 3530 has been calculated here for an average ilue gas loss of 25%, avalue of the constant losses a" of 5%,a mean specific heat cpm oi 0.333and a mean generating heat (io-tst) of 660 kcal. per kg.

of steam. Anindicating line S starts at the point G in line with the topof the triangular scale on the zero line of the scale. and runs to apoint H on the baseline of the triangular scale and a distance M awayfrom the maximum value of the instrument scale. This value Mcorretriangle.

sponds to the distance of the left starting point of the triangularscale to the vertical line 70%. The triangular scale shows thehorizontal divisions of the D-scale, reduced to the height ofthe Theleft side of the triangular scale intersects the indicating line S at avalue of D of nearly 3.0 checking the position of the RM .(Rt-t) pointerB on the above large instrument scale for D. The D-pointer A shows onthe line of 3.0 on the triangular rate of efficiency scale an efficiencyof '72.4% of the boiler, giving thereby the actual boiler eiciency.

This application is a continuation in part of my application Serial No.174,173, led November 12, 1937;

While several embodiments of the invention have been ldescribedl it willbe apparent that many changes might be made therein or that the methodmight be carried out in many diierent ways. It is accordingly notintended to limit the a' boiler comprising 'means forming a restrictioninvention to the exact forms described nor otherwise than by the termsof the appended claims.

What is claimed is:

1. Apparatus for determining the eiciency'of a boiler comprising meansfor measuring the ow of steam from the boiler, means for measuring theowfypf gas from the boiler, means for measuring the gas temperature,means for multiplying the gas iiow by the gas temperature to determinethe quantity of heat in the gas and means for dividing said quantity bythe steam flow;

2. Apparatus for determining the eiilciency of a boiler comprising meansfor measuring therflow of steam from the boiler, means for measuring theflow of gas from the boiler, means for measuringthe gas temperature,means for multiplying the gas ow--bythe gas temperature to determine thequantity of heat -in the gas, means to adjust the steam flow measurementto correct for feedwater temperature to determine the quantity of heatabsorbed in the steam, and

meter connected to said restriction to measure the steam flow, meansforming a restriction in a flue gas conduit leading from the boiler, a

flowmeter connected to said restriction to measure the gas iiow, athermometer in the conduit adjacent said last named restriction tomeasure the gas temperature, and means operatedby said flowmeters andsaid thermometer to combine the measurements in a ratio determining theboiler efliciency.

6. Apparatus for determining the eiciency of a boiler comprising meansforming a restriction in'a steam pipe leading from the boiler, aflowmeter connected to said restriction to measure the steam iiow, meansforming a restriction in a flue gas conduit leading from the boiler, aowmeter connected to said restriction to measure the gas flow, athermometer in the conduit adjacent said last named restriction tomeasure the gas temperature, means operated by said owmeters and saidthermometer to combine the.

measurements in a ratio determining the boiler efciency and means toadjust said ratio to correct forv feedwater temperature and for constantboiler losses. I

7. Apparatus for determining the eillciency of a -boiler comprisingmeans forming a restriction in a steam pipe leading from the boiler, aflowmeter connected to said orestriction to measure the steam iiow,means forming a` restriction in a flue gas conduitl leading from theboiler, a flowmeter connected to said restriction to measure the gasnow, a thermometer in said last named restriction to measure the gastemperature, means operated by said owmeters and said thermometer tocombine the measurements in a ratio means for dividing one of 'saidquantities by the other to obtain a quotient determining the efficiency.

3. Apparatus for determining the-elciency of a boiler comprising meansfor measuring the flow of steam from the boiler, means for measuring theflow of gas from the boiler, means for measuring the gas ,temperaturemeans for multiplying the gas flow by the gais temperature to determinethe quantity of heat in the gas, means to adjust the steam iiowmeasurement to correct for feedwater temperature to determine thequantity, of heat absorbed in the steam, means for dividing one of saidquantities by the other to obtain a quotient determining the efficiency4.and means to correct said quotient or constant boiler losses.

4. Apparatus for determining the eiciency of a boiler comprising meansfor measuring the flow of steam from the boiler, means for measuring theflow of gas from the boiler, means for measuring the gas temperature,means for multiplying the gas iiow by the gas temperature to determinethe quantity of heat in the gas, moans to adjust the steam flowmeasurement to correct for feedwater temperature to determine thequantity of heat 'absorbed in the steam, and means for dividing one ofsaid quantities by the other to obtain a quotient determiningtheeiliciency, and means to indicate the unburned gas flowing from theboiler whereby said quotient may be corrected for unburned gas.

5. Apparatus for determining the eiiicency of y determining the boilerefliciency, and means to indicate the unburned gas flowing from theboiler whereby said ratio may be corrected for incomplete combustion.

8. Apparatus for determining the emciency of a boiler comprising meansforming a restriction in a steam pipe leading from the boiler, a owmeterconnected' to said restriction to measure the steam f low, means forminga. restriction in a ue gas conduit leading from the boiler, a owmeterconnected4 to said restriction to measure the gas flow, a thermometer insaid last named restriction to measure the gas temperature, an electriccircuit, variable circuit controlling devicesA in said circuit connectedto said owmeters and said thermometer, and quotient responsiveindicating means connected to and controlled by said circuit to indicatethe boiler efliciency.

9. Apparatus for determining the efciency of a boiler comprising meansforming a restriction in a steam pipe leading from the boiler, ailowmeter connected to said restriction to measureA ture, 'an electriccircuit, variable circuit controlling devices in said circuit connectedto said flowmeters 'and said thermometer, a controlling device in saidcircuit adjustable tov correct for constant losses and for unburned gas'flowing from the boiler, and quotient responsive indicating meansconnected to and controlled by said circuit to indicate the boilerefliciency.

' WILHELM E. GERMER.

